Difflugia yorkui Nicholls, 2007
Diagnosis: Shell large, elongated oblong, usually with a distinct neck and covered with large and irregularly shaped siliceous particles except in the anterior region where particles are very small; test roughly circular (not compressed) in transverse cross-section, tapering towards both anterior and posterior ends from its widest point at about the middle of the test. Aperture relatively small and circular, . Organic basal material of the test (cement) organized in an open-meshed pattern of pores 0.3-0.8 µm in diameter separated by ribs 0.2-0.4 µm in width. With zoochlorellae. Nucleus ovular, densely filled with numerous small spherical nucleoli.
Dimensions: Nicholls (2007): Length 305-370 µm; width 140-162 µm; aperture 50-63 µm in diameter (n=12); my measurements: Length 222-460 µm (mean 365 µm); width 118-200 µm; aperture 56-101 µm (n=39).
Ecology: Freshwater; Canada, Netherlands (Naardermeer and several other locations).
Remarks: The identity of the Dutch shells was confirmed by Nicholls (pers. comm., 2021).
This species was also reported and pictured by Chardez, 1980, who called it D. pyriformis longicollis Gassowsky (see below).